How exactly did Chevrolet add all that torque plus 48 horsepower? The automaker essentially took a fine-tooth comb to the entire engine. Chevy says it changed 90 percent of the V8, and the cumulative effect of those small changes adds up to big increases.
As you might guess, the turbocharger is updated. The larger unit features electric actuation of the variable nozzle turbine (VNT), and what Chevy calls a double axle cartridge mechanism that separates the VNT moving parts from the housing. That helps with heat performance as well, with a claim that the exhaust side of the turbo can run continuously up to 1,436 degrees Fahrenheit. Helping that cause are six exhaust gaskets made of Inconel - an nickel alloy that contains chromium and iron – and upgraded stainless steel for the exhaust manifold.
Despite having the same cast iron cylinder block, albeit with some minor enhancements, the engine has new cylinder heads, pistons, piston pins, connecting rods, and crankshaft, which have all been upgraded to handle 20 percent higher cylinder pressures. Alongside the increase in pressure, Chevrolet also increased the cylinder head's structure with a honeycomb design. The pattern features high-strength aluminum with dual layer water jackets that not only improve strength, but also optimize water flow for better cooling. For 2017, the cylinder head also benefits from integrated plenum that aids the engine in getting more air under heavy loads. The cylinder head isn't the only component to get a minor update, as the pistons have a larger diameter pin for improved oil flow.
The same detailed improvements has been bestowed to the humble connecting rods (second in our hearts only to the inanimate carbon rod). The new design has the bolts oriented roughly 45-degrees to the rod instead of parallel. The angle split design, as it's called allows for easier passage through the cylinder. The connecting rods also feature a fracture split cap - a manufacturing method where the end of the rods are broken and fit back together instead of joined with a neat, machined surface - which increases the strength.
The upgraded turbo and new intake bring in more air, which allows for more fuel to get those peak power numbers. On that front Chevrolet placed a new, high-pressure fuel system consisting of a three-cylinder fuel pump, upgraded stainless steel low-pressure lines, and improved injectors. The new injectors can handle up to seven injections per combustion event, spraying fuel into to the engine at up to 29,000 psi.
Getting an engine to make good power figures is hard. Getting an engine to make good power figures reliably is extremely difficult. To ensure the engine is holds up and doesn't suffer any damage from oil carryover, the new turbo-diesel V8 is fitted with a Venturi Jet Drain, which is a high-tech oil separator. The separator utilizes boost from the turbocharger to pump oil back to the sump. The result ensures maximum performance from the engine during extended towing.
The engine isn't the only thing that has been altered as the six-speed Allison A100 transmission has been given a few new parts to handle more than 900 pound-feet of torque. The list includes improved seals and dampers in the torque converter, an upgraded torque converter clutch (TCC) valve, and a stronger output yoke.
With all these improvements, the 6.6-liter Duramax is basically a new engine, despite the carryover displacement. And it brings Chevrolet (and GM) right in line with Ford and Ram's output figures - at least until the next round of heavy-duty truck wars pushes things one step further.